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Computer simulations find the disordered needle in the crystalline haystack: Why smaller nanoporous materials are less flexible

 

New insight in the impact of the crystal size on the flexibility of nanostructured materials can aid the development of ideal nanosensors.

"Crystals are like people, it is the defects in them which tend to make them interesting!" The color and corresponding price of diamonds, the performance of semiconductor devices, or even the mechanical stability of metals. In each of these almost perfectly crystalline materials, material defects and other types of spatial disorder play a crucial role in the resulting material properties. Although this has been acknowledged and consciously applied for a long time—the above quote of Sir Colin Humphreys dates back to 1979—for nanomaterials the true impact of spatial disorder on their macroscopic behavior is in many cases still poorly understood.

For instance, flexible metal-organic frameworks (MOFs)—synthetic nanoporous crystals composed of both organic and inorganic building blocks—become less flexible the smaller the crystal. New research from the Center for Molecular Modeling (CMM) at Ghent University, published in Nature Communications, now demonstrates that this phenomenon originates from a newly identified type of spatial disorder in these materials.

Finding the disordered needle in the crystalline haystack

In general, material defects and spatial disorder only impact a very limited region in the otherwise crystalline material. As a result, it is not straightforward to clearly visualize this disorder. This challenge becomes even more formidable if the spatial disorder can also dynamically propagate through the material. Experimentalists then need high resolution techniques to reveal the instantaneous nanostructure of the material. For computational researches, the opposite challenge arises. As they often work with smaller and completely ordered models in their simulations, they need to develop new models that are sufficiently large to also capture spatial disorder.

Because of these challenges to clearly visualize dynamic spatial disorder in nanomaterials, it remained unclear until now which factors influence the flexible behavior of MOFs. Flexible MOFs form a class of materials that exhibit multiple stable states. Each of these phases can exhibit different material properties, just like defects alter the material properties of diamonds, semiconductors, and metals. Depending on a MOF’s phase, the material can adsorb more or fewer gas molecules, change its color, or become a better conductor. Flexible MOFs are attractive nanosensor materials as the phase of the material can be changed by altering the pressure or the temperature, or by forcing the material to adsorb molecules.

Although researchers already succeeded in visualizing the nanostructure of the different phases of a flexible MOF, given that these phases typically show crystalline order, it remained a mystery how flexible MOFs transition between these crystalline phases. Originally, the idea was that the structure of the material remained crystalline also during the phase transition, such that the phase transition occurs cooperatively throughout the material. However, this idea was indirectly contradicted by recent experimental results that demonstrated that smaller MOF crystals are less flexible than bigger ones.

From cooperative crystals to chaotic materials

To answer this apparent contradiction, researchers at the CMM systematically increased the crystal size of different flexible MOFs in their simulations. They observed that for sufficiently large MOF crystals, with a critical size above 10 nm, phase transitions no longer occur cooperatively. Instead, their simulations demonstrated that it becomes energetically more favorable for the material not to remain crystalline during the transition, but rather to show spatial disorder by allowing two phases to coexist simultaneously in the material. This phase coexistence results in local defects at the interfaces between the two phases (see red areas in the figure).

This work not only uncovers the mechanism behind the phase transition, but also explains why these phase transitions are hard to observe experimentally. The simulations indicate that the material defects that accompany the phase transition are very dynamic, which makes them very difficult to characterize experimentally. Therefore, this study also proposed different pathways that could be used to experimentally observe the spatial disorder demonstrated in this work. The study moreover demonstrated that it becomes energetically less favorable for smaller crystals to tolerate material defects. As a result, these smaller MOF crystals are also less flexible, in accordance with the recent experimental observations. These results now allow to consciously look for spatial disorder in flexible MOFs and to exploit this disorder to develop high-performing nanosensors.

More info

These results were published in Nature Communications:

Unraveling the thermodynamic criteria for size-dependent spontaneous phase separation in soft porous crystals
Sven M.J. Rogge, Michel Waroquier, and Veronique Van Speybroeck
Nature Communications, 10: 4842, 2019. DOI: 10.1038/s41467-019-12754-w

Contact

dr. ir. Sven M. J. Rogge, prof. em. dr. Michel Waroquier, prof. dr. ir. Veronique Van Speybroeck
Center for Molecular Modeling
Technologiepark 46, 9052 Zwijnaarde
E sven.rogge@ugent.be
M +32 (0)478 82 34 19

Prof. Van Speybroek highlighted as one of the strong Woman of Catalysis

The ChemCatChem journal, one of the premier journals in the field of catalysis, highlights the strong contributions of women-lead research groups in Catalysis Science. They placed 67 strong female researchers in the picture in a special issue: “Woman of Catalysis”. One of the invited authors is Prof. Veronique Van Speybroeck. She is leading the Center for Molecular Modeling, a multidisciplinary research center of about 40 researchers at the crossroads between physics, chemistry and materials engineering belonging to the Faculties of Sciences and the Faculty of Engineering and Architecture. Prof. Van Speybroeck is the recipient of two flagship grants from the European Research Council (ERC) and published more than 350 journal articles, amongst others in Science, Nature Materials, Nature Chemistry and Nature Communications. The ChemCatChem journal states that many exciting new advances in the field of catalysis science are contributed by female-led research groups. The Special Issue was conceived as a venue to celebrate the achievements of female researchers in the field of catalysis and highlight some of the best research led by women. With this action they also wanted to promote the representation of female researchers as speakers on international conferences or within editorial boards. With this special issue they wish to give visibility to Female research leaders to a broader catalysis community. Read the editorial here and the entire issue here.

Prof. dr. ir. Veronique Van Speybroeck gives her opinion on support and financing of researchers in FWO yearbook 2018

Traditionally, The Research Foundation - Flanders (FWO) distributes the FWO yearbook in the run-up to the Flemish and federal elections, a memorandum in which the FWO gives their idea on fundamental research in the next policy period. Veronique Van Speybroeck is the head of the Center for Molecular Modeling at Ghent University and has been arguing for strengthening fundamental research in the last years, along with colleagues from other Flemish universities. Together with nine other researchers and policy makers, she is included in the FWO yearbook. In a double interview with Herman Van Goethem, rector of the UAntwerpen, Veronique Van Speybroeck gives her vision on funding and procedures at the FWO and their influence on the career of researchers. Both argue for the importance of fundamental research in a knowledge-driven society. The full interview can be found here (in Dutch).

Yellow is not the new black: KULeuven-UGent discovery published in Science paves way for new generation of solar cells

A large international study led by the Centre for Membrane Separations, Adsorption, Catalysis, and Spectroscopy for Sustainable Solutions (cMACS) at KU Leuven (Dr. Julian A. Steele, Prof. Maarten B. J. Roeffaers, and Prof. Johan Hofkens) and with major contributions from the Center for Molecular Modeling (CMM) at Ghent University (Tom Braeckevelt, Dr. Kurt Lejaeghere, Dr. Sven M. J. Rogge, and Prof. Veronique Van Speybroeck) for the first time explains how a promising type of perovskites – man-made crystals that can convert sunlight into electricity – can be stabilized. As a result, the crystals turn black in appearance, enabling them to absorb sunlight. This is necessary to be able to use them in new solar panels that are easy to make and highly efficient. The collaborative study, spanning 11 research groups spread out over 8 institutes and 6 countries, was published in Science. The work was supported, among others, by 7 FWO postdoctoral fellowships, 1 FWO-SB fellowship, and 2 ERC grants, and was featured in articles by De Standaard and VRT NWS (both in Dutch).

 

Perovskites as promising solar cell materials

Perovskites are semiconductor materials that have many applications. They show particular promise in harvesting solar energy. Currently, most solar cells are made with silicon crystals, a relatively straightforward and effective material to process for this purpose. Perovskite-based devices offer the possibility for higher conversion efficiencies than silicon, but some of the most promising perovskites, namely cesium lead triiodide (CsPbI3), are very unstable at room temperature. Under these conditions, they have a yellow color, as the crystal does not form a perovskite structure (the way that atoms arrange themselves in the crystal). For the crystals to absorb sunlight efficiently and turn it into electricity, they should be in a black perovskite phase – and stay that way.

“Silicon forms a very strong, rigid crystal. If you press on it, it won’t change its shape. On the other hand, perovskites are much softer and more malleable,” explains Dr. Julian Steele of cMACS. “We can stabilize them under various lab conditions, but at room temperature, the black perovskite atoms really want to reshuffle, change structure, and ultimately turn the crystal yellow.”

 

Make perovskites stable again by thin film deposition

The international team of scientists discovered that by binding a thin film of perovskite solar cells to a sheet of glass, the cells can obtain and maintain their desired black form. The thin film is heated to a temperature of 330 degrees Celsius, causing the perovskites to expand and adhere to the glass. After heating, the film is rapidly cooled down to room temperature. This process fixates the atoms in the crystals, restricting their movement, so that they stay in the desired black form.

“There are three pillars that determine the quality of solar cells: price, stability, and performance. Perovskites score high on performance and price, but their stability is still a major issue,” says Steele. Scientists had already been observing for several decades that perovskites can retain their blackness after heating, but it was as of yet unclear why. “In our study, we chose CsPbI3 because its performance is very high,” Steel explains. “Additionally, it is one of the most unstable types of perovskites, which means it is sensitive to the method we describe, and should translate to other unstable perovskites.”

 

Unraveling the fundamental mechanism leading to stabilization

To understand the molecular mechanism underpinning these experimental observations, researchers at the CMM computationally investigated how this experimental procedure may stabilize the black and yellow phases of the perovskite. To this end, they mimicked the interfacial strain at the perovskite/glass substrate, and computationally determined how this strain affects the stability of both the black and the yellow phases. These computational results were vital to rationalize why the black phase is stabilized with respect to the yellow phase when fixating the perovskite as a thin film to a glass substrate.

How the bonding takes place exactly, is still a mystery, though there are hypotheses. “Normally, we would take a microscope with atomic resolution and directly have a look. However, that’s impossible with perovskites, as they don’t like to be looked at with such high-resolution imaging instrument.”

“Understanding how this mechanism works will help further research to ultimately develop solar panels that use pure perovskite crystals,” Steele says. “Since the entry level for processing perovskite-based solar cells is relatively low, they can be very beneficial for people in developing countries.” Additionally, perovskites can be used in LEDs, optical detectors, transistors, x-ray detectors and more.

 

Technical info

These results were published in Science:

Thermal unequilibrium of strained black CsPbI3 thin films
Julian A. Steele, Handong Jin, Iurii Dovgaliuk, Robert F. Berger, Tom Braeckevelt, Haifeng Yuan, Cristina Martin, Eduardo Solano, Kurt Lejaeghere, Sven M. J. Rogge, Charlotte Notebaert, Wouter Vandezande, Kris P. F. Janssen, Bart Goderis, Elke Debroye, Ya-Kun Wang, Yitong Dong, Dongxin Ma, Makhsud Saidaminov, Hairen Tan, Zhenghong Lu, Vadim Dyadkin, Dmitry Chernyshov, Veronique Van Speybroeck, Edward H. Sargent, Johan Hofkens, and Maarten B. J. Roeffaers
Science, dx.doi.org/10.1126/science.aax3878

 

ir. Tom Braeckevelt, dr. ir. Kurt Lejaeghere, dr. ir. Sven M. J. Rogge, prof. dr. ir. Veronique Van Speybroeck
Center for Molecular Modeling
Technologiepark 46, 9052 Zwijnaarde
M +32 (0)478 82 34 19

CMM publication highlighted in Matter

Matter devoted one of its first previews to highlight our recently published article providing an interactive machine learning approach to predict the mechanical stability of metal-organic frameworks. The preview, written by prof. Randall Q. Snurr of Northwestern University, not only focuses on the article's contribution to the development of mechanically stable MOFs, but also highlights the highly collaborative and multidisciplinary effort leading to the work:

"First, the 11 authors come from six different institutions and three countries. Rather than viewing each other as “competitors,” the authors have come together to solve an important problem, each research group bringing different expertise to the project. Second, the project both uses and creates open-source computational tools, including a database of MOFs, molecular modeling software, the ANN, and the web-based interactive data visualizer. Such sharing of codes, databases, and other tools can drastically speed up research and has other benefits as well, such as the potential for improved reproducibility of results. Finally, machine learning and other methods from data science—while perhaps overhyped at the moment—truly can lead to new ways of doing research. The results and insights developed in the work of Moghadam et al. were only possible because of the large amount of data generated by molecular modeling. It is possible that we are at the beginning of a new era of scientific research due to this shift toward team research, open-source tools, and data science."

 

Technical info

These results were published in the inaugural edition of the Cell Press journal Matter:

Structure-Mechanical Stability Relations of Metal-Organic Frameworks via Machine Learning
Peyman Z. Moghadam, Sven M. J. Rogge, Aurelia Li, Chun-Man Chow, Jelle Wieme, Noushin Moharrami, Marta Aragones-Anglada, Gareth Conduit, Diego A. Gomez-Gualdron, Veronique Van Speybroeck, and David Fairen-Jimenez
Matter, 1(1): 219-234, 2019. http://doi.org/10.1016/j.matt.2019.03.002

Dr. ir. Sven M. J. Rogge, prof. dr. ir. Veronique Van Speybroeck
Center for Molecular Modeling Technologiepark 46, 9052 Zwijnaarde
T +32 (0)9 264 65 75 | M +32 (0)478 82 34 19

Vacancies in the field of operando modeling of zeolite catalyzed reactions

The research group of Prof. Van Speybroeck, which is embedded within the multidisciplinary Center for Molecular Modeling, is looking for highly motivated and creative PhD candidates in the field of operando modeling of zeolite catalyzed reactions for industrially important processes. We are actively working on processes that will facilitate the transition from an oil based economy towards more sustainable chemical processes. Within this context we have a proven track record on the methanol to olefin process and alkene cracking and we are furthermore developing activities in the CO2 to hydrocarbons process and biomass conversion. To maintain our excellence level in these areas we are looking for new motivated researchers to join our team. All the projects are performed within an active network of prominent experimental partners. For all these chemical processes we aim to describe reactions and intermediates at operating conditions, thus at realistic working temperatures, loadings within the pores… To pursue these goals, we have developed a branch of first principle molecular dynamics methods that is recognized at the international level. You will be embedded within the Catalysis @CMM hub which is internationally recognized.

Go to: PhD positions | Postdoctoral positions | How to apply?

Vacant projects for PhD positions

1 PhD position in the topic:

'Zeolite-induced shape-selectivity for waste-free, highly regioselective catalytic arylation or alkenylation of aromatic C-H bonds'

Main host institution: Center for Molecular Modeling (CMM), UGent with Prof. Van Speybroeck. This is a position within the framework of a joint project with Prof. Dirk De Vos (KULeuven)

Within this project metal containing zeolites are investigated for the C-H activation of aromatic molecules in a shape-selective way. There is a strong pressure on the chemical sector to develop low waste routes, with a minimum number of process steps, for the production of high added value chemicals. Especially pharmaceutical production asks for products that are free of metal traces or residues of reactants, and isomerically pure. This provides a strong driver to invent new routes that activate C-H bonds, e.g. in aromatic molecules. However, aromatics often contain several C-H bonds, among which most catalysts do not discriminate. Consequently, most homogeneous catalysts (e.g. Pd) produce undesirable mixtures of isomeric product molecules. Together with our experimental partner Prof. Dirk De Vos (KULeuven) we have discovered new shape-selective zeolite catalyzed routes for C-H activation. Within this PhD topic, it is the intention to mechanistically explore from molecular level the reaction mechanism of the arylation reactions in various zeolites at operating conditions. To this end, we use a plethora of first principle molecular dynamics techniques. Our approach is unique as we simulate reactions at operating conditions thus fully accounting for the zeolite environment and dynamics and real process temperature conditions. We have a long standing collaboration with the De Vos group, which has already led to numerous high impact publications such as in JACS, Angewandte Chemie – International Edition,… The candidate will have the opportunity to actively participate in this successful partnership.

1 PhD position in the topic:

'Towards molecular control of electrophilic aromatic substitution reactions in homogeneous and heterogeneous environments through a combined ab initio molecular dynamics and conceptual density functional theory approach.'

Main host institution: Center for molecular Modeling (CMM), UGent with Prof. Van Speybroeck This is a position within the framework of a joint project with Prof. Frank De Proft (VUB- ALGC) and Prof. Bert Weckhuysen (Utrecht University)

The electrophilic aromatic substitution (SEAr) is a cornerstone reaction discovered by Friedel and Crafts in the 19th century. Despite its industrial importance for ethylbenzene production, the reaction mechanism is still debated. The proposed mechanistic pathway, relying on the formation of arenium ion intermediates, was recently challenged on experimental and theoretical grounds. The formation of the commonly assumed Wheland intermediate may critically depend on the reaction medium and process conditions. Herein, we will theoretically study SEAr intermediates in solvent and zeolite environments. Reactivity will be studied by an ingenious coupling of conceptual reactivity descriptors and construction of free energy profiles by means of advanced molecular dynamics methods. Such techniques allow following chemical transformations in-situ, thus closely mimicking experimental conditions. Complementary qualitative insights into reactivity will be obtained with a conceptual density functional theory approach. The combined approach will yield insights into governing SEAr reaction mechanisms and its dependency on the molecular environment and operating conditions. The theoretical work will be performed in close synergy with the group of Prof. Bert Weckhuysen, who recently spectroscopically identified the Wheland intermediate for benzene ethylation in zeolites. The outcome of the project will provide a general approach to unravel chemical reactivity in complex reaction environments.

Vacant positions for postdoctoral researchers

Postdoc positions in the field

'Operando modeling of zeolite catalyzed reactions for industrially important processes'

Postdoc positions are typically opened for one year but are potentially extendable. We especially welcome candidates with a strong track record who might become eligible to apply for Marie Curie postdoctoral fellowships or prestigious postdoctoral fellowships at our national funding agency (FWO).

Main host institution: Center for Molecular Modeling (CMM), UGent with Prof. Van Speybroeck

Topics eligible for postdoctoral positions:

The last decades, major efforts have been performed to induce the transformation from an oil based economy to the usage of alternative feedstocks such as natural gas and biomass to produce chemicals. This effort goes hand in hand with the development of cleaner processes to meet the mounting environmental concerns. The design of innovative and efficient catalysts for hydrocarbon conversion is of utmost importance to facilitate the transition to more sustainable chemical processes. We are actively looking for postdocs with a strong CV in the topic of the zeolite catalyzed reactions to reinforce our research in the on methanol-to-olefins and CO2 to hydrocarbons processes.

About the Center for Molecular Modeling (CMM)

The Center for Molecular Modeling (CMM) is a multidisciplinary research center of about 40 researchers from the Faculties of Sciences and Engineering and Architecture of Ghent University. The CMM, which is led by Prof. V. Van Speybroeck, is composed of an interdisciplinary research team which consists of chemists, chemical engineers, physicists, engineers in physics, chemical technology and bio-engineers. The Center focuses on frontier research in six major areas: nanoporous materials, modeling of solid-state physics, spectroscopy, many-particle physics, model development and bio- and organic chemistry.

The research team of Prof. V. Van Speybroeck focuses on modeling complex transformations in nanoporous materials such as zeolites, metal-organic frameworks and covalent organic frameworks. Our aim is to obtain physical and chemical insight into chemical reactions in and phase transformations of these nanoporous materials at operating conditions. This research fits into a large-scale investment we have started since 2015 within the framework of an ERC Consolidator Grant to use first principle molecular dynamics methods within the field of catalysis and nanoporous materials. To this end, we employ a complementary set of modeling techniques, either based on first principle methods such as density functional theory or on first-principle derived force fields, in combination with advanced sampling methods to unravel the governing free energy profile of various complex transformations.

The research team consists of various junior and senior researchers with various backgrounds which enables us to give a proper intellectual environment for the conducted research. We stimulate interaction between researchers with various backgrounds to enable groundbreaking research at the interface of physics, chemistry and materials science. The research is conducted in close collaboration with excellent experimental groups to guide the design towards new and promising functional materials. The research group is internationally regarded to be at the forefront in its field.

Who are we looking for?

We are looking for highly motivated and creative PhD candidates who have :

  • an excellent master’s degree or an international equivalent in the relevant fields of Chemistry, Chemical Engineering, Physics, Engineering Physics, Physical Chemistry or a related field.
  • a strong interest in sustainable energy conversion;
  • excellent research and scientific writing skills;
  • perseverance and an independent, pro-active working style;
  • the willingness to look beyond the borders of his or her own discipline and strong motivation to work in a multidisciplinary team;
  • excellent collaboration and communication skills (written and verbally) in English.

What can we offer you?

The selected candidate(s) will have the ability to attend various international conferences and to include research stays abroad in the most prominent international research teams in this field within the framework of his/her PhD or postdoc. Selected postdoc candidates will get the ability to strengthen their CV within the context of a multidisciplinary team. We especially looking for candidates with a strong track record and excellent study results.

How to apply?

It is the intention to fill these positions as soon as possible. Students who will obtain their Master degree in June/July are also eligible. Fill in the application form (download below) and send the form together with all required documents to cmm.vacancies@ugent.be

AttachmentSize
File Application Form_June 201999.17 KB

Looking back on the MOFSIM2019 workshop

The MOFSIM2019 workshop on April 10-12, 2019 in Ghent, Belgium was attended by over 110 modelers, including Ph.D. students, postdoctoral, senior researchers, as well as renowned experimentalists in the field of metal-organic frameworks (MOFs) and related porous materials.

This event was organized by prof. dr. Guillaume Maurin (Université de Montpellier), prof. dr. Bartolomeo Civalleri (Università degli Studi di Torino), and prof. dr. Veronique Van Speybroeck (Ghent University) and her team.

The two-day MOFSIM2019 workshop aimed to address the current state of the art, limitations, and perspectives on the computational tools applied to MOFs with a special emphasis on four main topics. During the workshop, renowned computational modelers shared their expertise in a plenary talk on each of the four topics, followed by presentations of invited speakers, opening the floor for plenary discussions open for every participant.

The workshop opened with a reception on the evening of April 10 in the former Dominician monastery ‘Het Pand’, owned by Ghent University. The workshop itself took place on April 11-12 in the Ghent University Aula in the historic city centre of Ghent.

On the first day, the topics Catalysis and adsorption in MOFs and Electronic properties and derived functions of MOFs were discussed. To this end, two renowned computational scientists shared their expertise during a plenary lecture: Laura Gagliardi (University of Minnesota) and Francesco Paesani (University of California San Diego). The day finished with a poster session, followed by a conference dinner at Restaurant Pakhuis.

On the second day, the MOFSIM2019 workshop addressed the topics Mechanical, thermal, and chemical stability of MOFs and Frontiers of MOF simulations towards longer length and time scales. These topics were introduced by François-Xavier Coudert (Chimie Paris-Tech) and Berend Smit (École Polytechnique Fédérale de Lausanne).

The invited speakers were: Dirk De Vos (KU Leuven), German Sastre (Universidad Politécnica de Valencia), Louis Vanduyfhuys (Ghent University), Thijs J.H. Vlugt (Delft University of Technology), Ben Slater (University College London), Thomas Heine (Technische Universität Dresden), Paolo Falcaro (Technische Universität Graz), Monique A. van der Veen (Delft University of Technology), Rochus Schmid (Ruhr-Universität Bochum), Jin-Chong Tan (University of Oxford), Peyman Z. Moghadam (University of Sheffield), Alessandro Erba (Università degli Studi di Torino), Rocio Semino (Université de Montpellier), Özgür Yazaydin (University College London).

A visual impression of the workshop is available through the banner below.

Click here to see more photos from the MOFSIM2019 workshop.

Thank you to all participants who made it a successful event!

Machine learning predicts mechanical properties of nanoporous materials

While metal-organic frameworks (MOFs) form promising materials to extract water from the air in the desert, to store dangerous gases or to power hydrogen-based cars, they are often very fragile. In collaboration with the University of Cambridge, researchers at Ghent University have developed a multi-level machine learning algorithm to computationally predict the mechanical properties of these materials and identify those MOFs that are sufficiently stable for practical applications.


Image courtesy of prof. David Fairen-Jimenez (University of Cambridge)

Molecular K’NEX

Similar to K’NEX or Lego sets, MOFs are functional structures assembled from a combination of building blocks. By precisely selecting building blocks with appropriate properties and assembling them in a periodic material, researchers can design MOFs with vastly different structures and functionalities for applications in fuel storage, detoxification of hazardous environments, or carbon capture. However, as with K’NEX or Lego, the stability of the MOF is a crucial design parameter that can literally make or break the material.

For MOFs, this fragility originates from their highly porous structure and massive surface area: a MOF the size of a sugar cube laid flat would cover an area the size of six football fields. While this makes them highly effective as adsorption and storage devices, as highlighted in this EOS blog article (in Dutch), their internal pores make them also very prone to structural collapse under pressure.

MOFs under pressure

As MOFs are generally synthesized in powder form, the powder needs to be put under pressure and formed into larger, shaped pellets to be of any practical use. Due to their porosity, many MOFs are crushed in this process, wasting both time and money.

To address this problem, researchers at the University of Cambridge, Ghent University, and the Colorado School of Mines under supervision of prof. David Fairen-Jimenez and prof. Veronique Van Speybroeck developed a machine learning algorithm to predict the mechanical properties of thousands of MOFs so that only those with the necessary mechanical stability are manufactured.

Neural networks to predict stable MOFs

The project, spearheaded by dr. Peyman Z. Moghadam and dr. Sven Rogge, used a multi-level computational approach in order to build an interactive map of the structural and mechanical landscape of MOFs. First, they used high-throughput molecular simulations for 3,385 MOFs. Secondly, they developed a freely-available machine learning algorithm to automatically predict the mechanical properties of existing and yet-to-be-synthesised MOFs.

The researchers have launched an interactive website where scientists can design and predict the performance of their own MOFs. This tool will help to close the gap between experimentalists and computationalists working in this area, as it allows researchers to access the tools they need in order to work with these promising materials.

Technical info

These results were published in the inaugural edition of the Cell Press journal Matter:

Structure-Mechanical Stability Relations of Metal-Organic Frameworks via Machine Learning
Peyman Z. Moghadam, Sven M. J. Rogge, Aurelia Li, Chun-Man Chow, Jelle Wieme, Noushin Moharrami, Marta Aragones-Anglada, Gareth Conduit, Diego A. Gomez-Gualdron, Veronique Van Speybroeck, and David Fairen-Jimenez
Matter, http://doi.org/10.1016/j.matt.2019.03.002

Dr. ir. Sven M. J. Rogge, prof. dr. ir. Veronique Van Speybroeck
Center for Molecular Modeling
Technologiepark 46, 9052 Zwijnaarde
T +32 (0)9 264 65 75 | M +32 (0)478 82 34 19

Steven Vandenbrande successfully defended his PhD

Steven Vandenbrande successfully defended his PhD on May 8th, 2019. His dissertation entitled 'Understanding Noncovalent Interactions in Force Fields through Quantum Mechanics: Application to Gas Adsorption in Metal-Organic Frameworks', was supervised by Prof. Dr. ir. Veronique Van Speybroeck and Prof. Dr. ir. Toon Verstraelen.

A summary of his research is provided below:

Simulations at the atomic scale require an accurate description of interactions between atoms. An important consideration when modeling these interactions, is the computational burden of the model. Even when using the most powerful computers, an exact solution of the relevant equations is out of reach for nearly all systems of interest. The main methodological advancement proposed in this dissertation is therefore a novel model for interacting atoms, seeking a balance between accuracy on the one hand and computational tractability on the other. By first decomposing the total interaction energy into meaningful components, the model is built on a solid physical foundation. A second unique feature is the limited amount of empirically fitted parameters, which ensures robustness and reliability. The proposed model was used to study the adsorption of gas molecules in metal-organic frameworks. These materials offer promise for applications such as carbon capture and sequestration. Simulations employing the earlier developed model enabled to gain insight into such processes, in this way contributing to the further development of metal-organic frameworks.

Congratulations, dr. Vandenbrande!

Prof. dr. ir. Van Speybroeck is a speaker on May 3rd at the UK Catalysis Hub Spring Conference 2019

Prof. dr. ir. Veronique Van Speybroeck is one of the speakers at the UK Catalysis Hub Spring Conference 2019, taking place on May 2nd & 3rd, 2019. Her talk on the second day is entitled ‘Unraveling the nature of reactive intermediates and prevailing pathways within zeolite catalysis by first principle molecular modeling’. The Conference will take place on the Harwell Campus, located just south of Oxford.

More info: https://ukcatalysishub.co.uk/uk-catalysis-hub-spring-conference-2019/

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